Bone conduction receiver



Feb 4, 19,41- s. F. LYBARGER 2,230,499

.BONE CNDUC'I-ION RECEIVER Filed oct. 5, 193e 2 sheets-sheet 1 i y "gy/l 5 /A//ll/ v 1v `17 aad/MM. @wf 0.9t P @07m- @ma r M ATTORNEYS.

Feb. 4, 1941. s. RLYBARGER 2,230,499.

BONE CONDUCTION v RECEIVER Filed oct. 5, 19584 2 sheets-sheet 2 P-'ggf 6, P

33 ngik- ,Y A\\\\I\I) Il ll/l' w/T/vssfs INVENTOR.

m. BY WJ. Ww

1 44 ATToRNfgYs.

Patented Feb'. n, 1941 UNITED STATES PATENT OFFICE accosta BoNE coNDUc'rroN nncmvun Lybarger 'Application october 5, 193s, f 1 :i

16 (otite-1er) This invention relates`to hearing-aid receivers for hard-of-hearinglpecple, and more particularly to bone conduction receivers oi' the direct action type.

There are two general types of bone conduction receivers. In the indirect or inertia reaction type of vibratory mem-ber is directly supported by a head-bend or other means against a hearing inducing bone of the user where it is w vibrated by reaction forces generated -bya oatf ing electromagnetic body supported by the vibratory member. In the direct action type the electromagnetic means is directly supported by the head-band and in Iturn supports the vibra' 5 tory member against the hearing inducing bone. This latter type of receiver is sometimes referred to as the button type because the vibratory member often resembles e button vibra/ted by the electromagnetic means.

In the inertieJ reaction-type receiver it is immaterial so far es the air gap between the vibratory member and electromagnetic means is concerned, as to how much pressure is applied to the vibratory member bythe head-band, because the band is connected directly to the vibretoi'i7 member and therefore this pressure cannot decrease the widthof the air gap. On the other hand, a serious objection to direct action receivers known heretofore has been that the pressure of the head-band 'against the electromagnetic means forces Ait toward the vibratory member and thereby decreases the air gap. Attempts Vto overcome this dimculty by initially n w the air gap greater than it should be so that it will be decreased to the correct width when the receiver is in position generally have not been successful because the pressure applied to the receiver by its supporting means varies with dierent individuals, due to distortion of the supporting means, or to diilerences inthe shape ot heads.

Although the problem may be solved to some extent by stiiening the resilient support for the vibratory member so that it will oier greater re sistance to closing of the gap, this brings about other` disadvantages, such as impairment of rel spouse characteristics, especially in the low frequency'band.

The `importance of`min`imizing or eliminating the effect of .the .head-band pressure on the air gap will'be more evident when the following facts are considered.V .Headband pressure generally varies with different individuals from about 5 to 15 ounces, a, desirable air gap is of Ithe'order of .003" (.0075 cm.) ,Y andthe stiffness of the spring system within most receivers as measured at the air gap should be of the order of 30 to 1.00X10s dynes per cm. if eilicientY operation is to be ob tained. If, for example, this stiffness is 30x10*3 dynes per cm., a change in head-band pressure of one ounce (27,800 dynes) will cause a change of 27800 @Toe-0.00035 Cm.. in the air gap spacing. A change of 10 oz. in pressure would cause a change of .0035 cm.. or almost half of the desirable air gap spacing.

In prior types of receivers the effective mass of the .heed-band yoke is added directly tothe ed'ective mess ci the receiver case because the yoke is attached to the case at a point where the piitude of vibration is substantially greatest. The resulting total eiective mass is often too great to permit of the desired frequency response characteristics in the middle frequency renge.

Consequently, direct" action bone conduction receivers have never been very satisfactory heretofore when held in position by a head-band or the like.

It is among the objects of this invention to provide a direct ection bone conduction receiver for hearing aids and the like inY which the tendency of the pressure of its supporting means to aiiect .the spacing of its airfgap is greatly decreased, and can be eliminated entirely if desired, without impairing the desired response characteristics. Another object isto provide a. closed housing for the electromagnetic system of the receiver in which the vibratory member forms one wall of the housing. v

In accordance-with this invention a. substan-f tially rigid vibratory member adapted to be pressed against a hearing inducing bone of the hard-of-hearing person, such 4as the mastoid bone, is disposed adjacent one end .of Ithe polepiece of an electromagnet with an air gap between them. The means that connects the opposite end of the pole-fpiece to the vibratory 1nem4 ber and thereby supports it has a resilient portion spaced laterally from the air gap. 'I'he Vibratory member is held in operative position by suitable supporting means, such as a head-band, irresiliently connected with the pole-piece so that the pole-piece can not vibrate relative to its support. The pressure by which the supporting means presses the vibra/tory member toward the bone is applied to the receiverat a point between its air gap .and the abqre-mentioned-resilient portion whereby .the effect of this pressure on, the

.width of the air gap is decreased. By providing tendency of .the supporting pressure to alter the air gap can be controlled to the point `of elimination. This desirable result is obtained without impairing in any noticeable way the response characteristics of the receiver. Preferably, the

vibratory member itself forms a cover for .the case that houses the electromagnetic means. A s the v-ibr'atory member must be spaced from the side walls of the case in order to vibrate relative thereto, the intervening space is sealed vby a highly resilient gasket to keep out dust and dirt.

The invention is illustrated in the accompanying drawings i'n which Fig. 1 is a side view of my receiver as applied to the head behind an ear; Fig. 2 is an enlarged plan view of the receiver as seen when it is lying with its vibratory member face down; Fig. 3 is a longitudinal section taken on the line III- III of Fig. 2; Fig. 4 is a trans-f verse section taken on the line IV-IV of Fig. 2;

Fig. 5 is a diagrammatic illustration of .the foregoing receiver; Figs. 6, 'I and 8 are views similar to Fig. 3 ofthree modified embodiments of this invention;r and Fig. 9 is a plan view of the receiver of Fig. 8 minus its case.

As viewed in Figs. 2 to 4 of the drawings, an integral case I, which is generally rectangular in cross section, has a top and depending side and end walls and an open bottom. Mounted in this case is electromagnetic means for driving a vibraiory member in accordance with variations in electric current caused by a microphone responding to sound waves. 'Ihe electromagnetic means or system includes a permanent bar magnet 2 to one end of which is secured a metal pole-piece 3 that has a portion extending substantially at right angles to the magnet and towards the open bottom of the case. The inner end of the polepiece is preferably disposed between the magnet, to which it is connected by screws I, and the top of the case. The pole-piece and magnet are rigidly attached to' the top of the case by screws 6 threaded into the pole-piece, and by screws 1 connected to a spacer member 8 between the opposite end of the case and the magnet to which the spacer member is attached by screws 9. The.

outwardly. projecting portion of the pole-piece is encircled by an electromagnetic coil vIl connected by wires I2 to metal spring strips I3 secured at one end to the sides of the case with their other ends projecting partway across a pair of openings I4 through the adjoining end wall of the case. These openings are adapted to receive electric plugs I8 that engage springs I3 and connect them with the microphone or ampliiler unit (not shown) of the hearing-aid sysein.'

Extending across the open bottom of the case and forming a cover therefor is a rigid plate-like button or vibratory member I1 adapted to engage a hearing inducing bone, such as the mastoid bone, of a hard-of-hearing person. Of course, engagement with a bone means contact with the skin overlying the bone. This vibratory member is supported from the interior of the case in predetermined spaced relation with the outer end of the pole-piece by means of an elongate member Il which is resilient wholly or in part to permit the vibratory member to bevibrated by the electromagnet. As the vibratory member is rigid, it must also be spaced a slight distance from case I so that its movements will not be prevented by the case. This space is closed by a highly resilient gasket -IS of felt, rubber, sponge rubber, or the like that seals out dust and dirt without impairing the operation of the receiver. Being a direct action-type receiver, the vibratory member is pressed against the head or other bone structure by the case through elongate member d8, the case being directly supported by suitable means, such as a head-band.

As shown in Figs. 1 and 2, the band includes a curved strip of spring metal adapted to ilt over the head, and a yoke 2| pivotally connected to the metal strip and straddling the case. The ends of th yoke are provided with pins v2'2 that are pivotally mounted in holes 23 in the opposite sides of the case so that the case can tilt vertically relative to the yoke to better adjust itself tothe contour of the head. The outer surface of the vibratory member is preferably curved longitudinally to give a greater area of contact with the head sd as to rest more comfortably against it, and also to better retain the vibratory member in position. 'f

It is a. feature of 'this invention that this receiver is so constructed that it can be 'supported' of the elongate member is' connected to magnet bar 2 at the end opposite to the pole-piece by screws I. Also, the end portions ofthe elongate member are oii'set whereby its straight central portion is spliced from both the vibratory member and the magnet bar. By making elongate member il of magnetic metal, its outer end can serve as the armature for the electromagnetic system when extended across the end of the pole-piece as shown in Fig. 3. In spite of the pole-piece being rigidly mounted in the case, it can be sprung away from magnet -2 a very slight amount by set screw 2l to increase the width of air gap 20.

Even though the elongate member 1s resilient f throughout its length, most of its bending during vibration of 'the vibratory member occurs near its inner end because the leverage exerted at that point is greater than at any other point. For the same reason the elongate member bends adjacent its outer end in case the head-band -pressure forces its inner end toward the vibratory member. As it is desirable for the purposes of this invention that such bending of the elongate member be more or less localized at two longitudihally spaced points rin this manner, its straight central portion is preferably provided with longitudinally extending corrugations '29l to stiien it so that it will not bend appreclably. Nevertheless, wherever it states hereinvthat the elongate member is provided with longitudinally spaced resilient portions, it is to be understood, unless the contrary is stated, that the intermediate portion may also be resilent but that the maior or entire amount of the bending of the elongate member occurs substantially only at the spaced resilient points for the reasons given above.

Fig, is a diagrammatic representation of Fig. 3 for the purpose of more clearly illustrating my invention by showing the reaction of the receiver to the head-band when it presses the receiver against the head. Line 3 represents the polepiece, line 2 the bar magnet, line II the vibratory member, line I8 the connecting elongate member, and dots J and K the resilient end portions or springs of the elongate member. It will be seen from Fig. 5 that if the head-band were attached to the receiver at a point where it would exert pressure in the upper end of pole-piece 3- directly above air gap 25, it would tend to push shortened-and therefore the pressure can notI flex the spring so easily. As most of the springing during vibration occurs at J, the amplitude of vibration of the vibratory member is greatest at the farther end, adjacent the airgap. Therefore,

it is desirable to maintain good contact between between springs J and K, the tendency of thatpressure to push the pole-piece toward the left end of the vibratory member is offset or counteracted by the tendency of the reaction P'. to that force to push the right end of the .vibratory member toward the right end of the magnet. The result is that the air gap remains more or less constant. The point of pressure application at which any tendency of the pressure to affect the air gap is.eliminated can be determined. This depends on the relationcof lthe length of line 2 to the length of line Il between the .air gap and spring K, and the relation of the resiliency of spring J to that of K. The resiliency oi' K can,y

be less than J without materially affecting the vibration characteristics of the instrument because most of the vibrational springing occurs at J:

In the modification disclosed in Fig. 6, the vibratory member i'I is supported from permanent magnet 2 in the same general manner as the has a straight portion and an offset end secured to the magnet by screws 9. The outer member 33 is straight from end to end and is secured to the vibratory member opposite the pole-piece by screws 34. Bending of these two members can be concentrated at longitudinally spaced points by providing each of them with a transverse notch or groove 36. The grooves must not be so deep that any appreciable effect on the magnetic flux is introduced because of magnetic saturation at .these points. The grooves are also useful as a means of adjusting the values of theeffective stiffness of the members at the grooves. Of course, the overlapping portions'of these members make the central portion of the elongate supporting means rigid.

To permit relative movement-of the vibratory member and stili central portion of the elongate lmeans toward and away from each other so that pressure of the head against the vibratory member will compensate for the pressure of the headband on the case, as far as `the air gap is cons cerned, member 33 is spaced from the vibratory member by a spacing washer 3l at its xed end. The spacing of the air gap can be adjusted by means of a set screw 38 vto which access can be' gained at any time through an opening 39 in the vibratory member which is normally closed by a plug B0. This two-piece supporting member permits separate testing and adjustment of members 32 and 33 before assembly in a sornewhat` easier manner than possible with av one-piece spring. Fig. 'I illustrates a receiver of this character ink which the means for supporting the vibratory member consists of a one-piece elongate member or spring 4I.'

2, but the remaining portion of the spring is straight. This straight portion extendsparallel to thev vibratory member to which it is connected by screws d2 between the air gap and its opposite end, and may extend beyond this point of attachment so as to form an armature beneath lthe pole-piece. This extension should be short enough to act substantially as a rigid member. The spring is spaced from the vibratory member by a spacing washer t3 to permit movement of the spring and vibratory member relative to each other as previously described. If desired, this spring may be provided with grooves to concentrate bending at longitudinally spaced points, but it will work satisfactorily without notches because the distribution of the bending moment stresses in it is such as to provide, in effect, a division of the bending of the spring into two longitudinally spaced portions as is the case with spring i8 shown in Fig. 3. Attachment of the spring to the vibratory member at the right of the air gap has some advantage in that the attachment point is nearer the center of the receiver.

A further modification of the invention is shown in Figs. 8 and 9 in which the supporting spring member 5i is in no way associated with the magnetic circuit of the receiver. This makes it possible for a non-magnetic spring to be used, and also permits the use of steels which have good mechanical properties but whose magnetic properties are poor. In this embodiment a compact vbipolar electromagnet is formed from a. perma- The inner end of thelspring is oifset and rigidly connected to permanent magnet nent magnet 52 having at its opposite sides del pending pole-pieces 53 carrying coils 55. The pole-pieces are connected to the magnet by nonm'agnetic screws 56 passing therethrough and also through the forwardly projecting arms of a bracket 5l by which the electromagnet is attached to the inner end of the substantially U- shaped spring 5I, :The inner leg of the spring is rigidly secured to the top of the case by screws 58, while its outer leg is spaced from the vibratory member by means of a washer 59 beneath ythe magnet at which point the spring is secured to the vibratory member by screws 5 I'. These screws also connect an armature 62 of good magnetic material to the end of the spring to complete the magnetic circuit of the receiver. The spring may be provided in its outer leg and inits intermediate portion with grooves 63 and 66 to concentrate its bending at those two points.

Fig. a also illustrates the use of another type A resilient because it can open and close with the vibrations of the receiver. i

It will thus be understood that in a receiver` made in accordance with this invention the tendency of the head-band pressure to alter the air gap-can be reduced so that it is no longer objectionable, or it can be eliminated entirely. Another advantage, especially where it is desirable to increase response, in the middle frequency range, resulting fromthe same construction is that the eiiect of the added mass of the headband yoke vis minimized because the head-,band is attached to the receiver at a point where the amplitude of vibration of the case is relatively small. By merely attaching the head-band to the vibratory member instead of to the case, and placing the case against the head, the eiective vibratory mass can be still. further reduced'in order to increase response in the middle frequency range. According to the provisions of the patent statutes I have explained the principle and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within` the scope of the appended claims, the invention may be practiced otherwise than as specically illustrated and described.

I claim:

1. A direct action bone conduction receiver comprising a pole-piece, a vibratory member adjacent the pole-piece, elongate means connected at one end to the vibratory member adjacent` the pole-piece and extending away from both of them, and rigid means connecting the pole-piece and the opposite end of the elongate means, said elongate means having longitudinally spaced'resilient portions, the receiver being formed for connection to. supporting means that applies pressure .to said rigid means at a location between said resilient portions for holding the vibratory member against a hearing inducing bone of the user.

2,. A direct action bone conduction receiver adapted to be supported by a head-band or the like, comprising a pole-piece, a plate-like vibratory member adjacent the pole-piece, a resilient member connected only to the end of the vibratory member adjacent the pole-piece and extending away from both of them, and rigid means connecting the pole-piece and the far end of the resilient member, said rigid means having a porj tion located between the ends of the resilient `member for connection to the head-band.

3. i The combination with a resilient head-band for supporting a hearing-aid receiver against the head of the user, of a direct action bone conduction receiver comprising a pole-piece, a vibratory member adjacent the pole-piece, elongate means connected at one end to the vibratory member adjacent the pole-piece and extending away from both of them, and rigid means connecting the pole-piece and the opposite end of the elongate means, said elongate means being provided with longitudinally'spaced transverse grooves to form spaced resilient areas, thehead-band being connected to said rigid means at a location between the resilient areas of said elongate means for pressing the vibratory member against a hearing inducing bone of the user.

4. A direct action bone conduction receiver 75 comprising a pole-piece, a vibratory member adjacent the pole-piece, elongate means connected I at one end to the vibratory member adjacent the pole-piece and extending laterally therefrom,-

means spacing saidend of the elongate means from the vibratory member, the opposite end of said elongate means being offset from the vibratory member, and rigid means connecting the pole-piece and said offset end of the elongate means, said elongate means having longitudinally spacedI resilient portions between said ends, the receiver being formed for connection to supportvmeans disposed between only said end of the elongate means and the vibratory member, the opposite end of said elongate means being oiset from the vibratory member, and rigid means connecting the pole-piece and said offset end of the elongate means, said elongate means having longitudinally spaced resilient portions between said ends, the receiver' being formed for connection to supporting means that applies pressure to said rigid means at a location between said resilient portions for holding the vibratory member against' ahearing inducing bone of the user.

6. A .direct action bone conduction receiver comprising a pole-piece, a vibratory member adjacent the pole-piece, elongate means having a substantially straight portion extending along the vibratory member away from the pole-piece, means at one side of the pole-piece for spacing said elongate means from the lvibratory member, means for connecting said elongate means and spacing means to the vibratory member, the oppositenend of said elongate means being oiset from the vibratory member, and rigid means connecting the pole-piece and said offset end of the elongate means, said elongate means being resilient and adapted to ilex principally in two 1ongitudinally spaced portions between said ends, the receiver-being formed for connection to supporting means that applies pressure to said rigid means at a location between said longitudinally spaced portions for holding the vibratory member against a hearing inducing bone of the user.

7. A direct action bone conduction receiver comprising a pole-piece, a vibratory member adjacent the pole-piece, elongate means connected at one end to the vibratory member adjacent the pole-piece and extending away from both of5 them, rigid means connecting the pole-piece and the opposite end of the elongate means, said elongate means having longitudinally spaced resilient portions, and including overlapping members, means ing means that applies pressure` to said rigid for connecting them together, and means for springing them apart a slight amount to vary the spacing of the air gap, the receiver being formed for connection to supporting means that applies pressure to said rigid means at a location between said resilient portions for holding the vibratory member against a hearing inducing bone of the user.

8. A direct action bone conduction receiver comprising a. pole-piece, a vibratory member adjacent the pole-piece with an air gap between them, a substantially U-shape memberhaving a leg extending substantially parallel to the vibratory member in spaced relation thereto with its end connected to the vibratory member adjacent one end of the pole-piece, the end of the opposite leg being connected to the pole-piece,

.5 said U-shape member having longitudinally spaced resilient portions, the receiver being formed for connection to supporting meansthat applies pressure to said opposite leg oi' the U- shape member at a location between said resilient 1o portions for holding the vibratory member against a hearing inducing bone of the user..

9. In combination, a direct' action bone conduction receiver comprising'a pole-piece, a vibratory-member adjacent the pole-piece, elongate means connected at one end to the vibratory member adjacent the pole-piece and having a .portion extending between them and forming an armature spaced from the pole-piece, the remainder of said means being spaced from the vibratory member, rigid means connecting the pole-'piece and the opposite end ot the elongate Ameans, said elongate means having longitudinally spaced resilient portions, and supporting means connected to the receiver at a location between said resilient portions of the elongate means -for applying pressure to said rigid means to hold thewibxatory member againstv a hearing inducing bone of the user.

10. In combination, a direct action bone conduction receiver comprising a pole-piece, a vibratory member adjacent the polepiecee1ongate means connected at one end to the vibratory member adjacent the pole-piece and extending away from both of them. rigid means connecting the pole-piece and the opposite end of the elongate means, said felongate means having longitudinally spaced resilient portions, and supporting means adapted to apply pressure to'said rigid means at a location substantially midway be- 40 tween said resilient portions for holding the vibratory member against a hearing inducing bone of the user. L

11. In combination, a direct action bone conduction receiver comprising a pole-piece, afvibraeli tory member adjacent thevpole-piece. elongate means connected at one end t o the vibratory member adjacent the pole-piece and extending away from both of them, rigid means connecting the pole-piece and the opposite end' ot the elongate means, said elongate means having longitudinally spaced resilient portions, and means for supporting the receiver adjacent a hearing inducing bone ci the user and i'or pressing the vibratory member toward the bone, said supportingmeansbeingccnnectedtosaidrisidmesns substantially at the location between said resilient portions of the elongate means atiwhich the tendency o!y the pressure of the supporting means to torce the pole-piece vcloser to the vibratory 0 member is substantially countersctcd by the tendency of the reaction to that pressure to spread them farther apart.' Y

12. A direct action bone conduction receiver comprising al vibratory member, a permanent u bar magnet spaced therefrom substantially par aileltheretaapole-piececonneetedtocneend or themagnet and extendingtoward the-vibratory member. an elongate memben having resiii-J torymemberagainstahcacfinginducingbonen! 7( the user with pressure applied to themosnot at a location between the resilient ends of the elongate member. v

v13. A direct action bone conduction receiver comprising a case open at one side, electromag- Anetic means rigidly mounted in one end of the 5 case. -a resilient member rigidly connected to the other end of the case and extending freely toward said one end and the openside of the case. and a rigid vibratory member extending across the openside oi the case and having only l0 its end adjacent said electromagnetic means rigidly mounted on the outer end portion of said resilient member, the case being formed for attachment to means for supporting it adjacent a hearing inducing bone of the user and for press` 15 ing the vibratory member toward the bone with a pressure 'applied to the case at a location between the ends of the resilient member, whereby the eiect of said pressure on the spacing of thev air gap is reduced. 20

l 14. A direct action bone conduction receiver comprising a case open at one side, electromagnetic means rigidly mounted in one end oi the case. a resilientmember rigidly connected to the` other end of the case and extendingdiagonally 25 toward said electromagnetic means and the open side of the case. a rigid vibratory member extending across the open side of the case and rigidly mounted on the outer end portion of said resilient member only at a location adjacent said v30 electromagnetic means, and a highly resilient gasket disposed between the vibratory member and the wall of the case surrounding its open side for sealing thespace between them. the case being formed for attachment to means ,for supporting it adjacent a hearing inducing bone of A the user and for pressing the vibratory member toward the bone with a pressure ,applied to the case at a location between the ends of the resilient member, whereby the eiIect o1 said pres- 40 sure on the spacing or the air gap is reduced.

resilient member only at a location adjacent said 5 electromagnetic means. the case-beingprovided in its sides with a pair o! oppodtely disposed openings located between the ends ot the resilient member, and a head-band having a yoke -wxtn inwardly projecting pins that extend into said Wellin- 16. In combination, a case open at one side, electromagnetic means rigidly mounted in one end oi the case. a resilient member rigidly connectedtotneotnerendortnecaseansextens- 0 ing treelytowardsaidoneend and theopenside ot the oase. said member having more resiliency in two longitudinally spaced portions than elsewhere. and a rigid vibratory member extending aero the open side ot the caseand rigidly 5 mounted on the outer end portion c! said resilient member. the case being Provided in its sides with a pair o! oppositelydisposed openings located between the ends-ot the resilient member substantially midway between its moet rennen: 7 portions, and a head-band having, a, yoke with inwardly projecting pins that extend into said slimme reprennent.' s 'Y' 

